Workload Management

Running applications in Kubernetes means choosing the right workload resource for the job. This lesson covers Deployments, StatefulSets, DaemonSets, Jobs, and CronJobs, along with resource management, QoS classes, and pod disruption budgets.

---

Workload Resource Comparison

Resource	Use Case	Pod Identity	Scaling
Deployment	Stateless apps (web servers, APIs)	Interchangeable	Horizontal
StatefulSet	Stateful apps (databases, caches)	Stable, ordered	Ordered
DaemonSet	One pod per node (monitoring, logging)	Per-node	N/A
Job	Run-to-completion tasks	Temporary	Parallel
CronJob	Scheduled tasks	Temporary	Per schedule

---

Deployments

Deployments manage stateless applications through ReplicaSets. They support rolling updates, rollbacks, and horizontal scaling.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-api
  labels:
    app: web-api
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web-api
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1          # 1 extra pod during update
      maxUnavailable: 0    # zero downtime
  template:
    metadata:
      labels:
        app: web-api
    spec:
      containers:
        - name: api
          image: myapp/web-api:v2.1.0
          ports:
            - containerPort: 8080
          resources:
            requests:
              cpu: 250m
              memory: 256Mi
            limits:
              cpu: 500m
              memory: 512Mi
          livenessProbe:
            httpGet:
              path: /healthz
              port: 8080
            initialDelaySeconds: 10
            periodSeconds: 15
          readinessProbe:
            httpGet:
              path: /ready
              port: 8080
            initialDelaySeconds: 5
            periodSeconds: 5

Deployment Operations

# Apply a deployment
kubectl apply -f deployment.yaml

# Check rollout status
kubectl rollout status deployment/web-api

# View rollout history
kubectl rollout history deployment/web-api

# Roll back to previous version
kubectl rollout undo deployment/web-api

# Roll back to a specific revision
kubectl rollout undo deployment/web-api --to-revision=3

# Scale the deployment
kubectl scale deployment/web-api --replicas=5

---

StatefulSets

StatefulSets provide stable network identities and persistent storage for stateful applications.

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: postgres
spec:
  serviceName: postgres
  replicas: 3
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres
    spec:
      containers:
        - name: postgres
          image: postgres:16
          ports:
            - containerPort: 5432
          volumeMounts:
            - name: data
              mountPath: /var/lib/postgresql/data
          env:
            - name: POSTGRES_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: postgres-secret
                  key: password
  volumeClaimTemplates:
    - metadata:
        name: data
      spec:
        accessModes: ["ReadWriteOnce"]
        storageClassName: fast-ssd
        resources:
          requests:
            storage: 50Gi

StatefulSet pods get predictable names: postgres-0, postgres-1, postgres-2, and each gets its own PersistentVolumeClaim.

StatefulSet vs Deployment

Feature	Deployment	StatefulSet
Pod names	Random suffix	Ordered index (0, 1, 2)
Startup order	Parallel	Sequential
Storage	Shared or none	Per-pod PVC
DNS	Via Service only	Headless per-pod DNS
Rolling update	Any order	Reverse ordinal order

---

DaemonSets

DaemonSets ensure exactly one pod runs on every (or selected) node. Ideal for node-level agents.